1. Field of the Invention
The present invention relates to heating apparatus and in particular to apparatus for heating the operator's cabin of a machine driven by an internal combustion engine using heat extracted from hot engine sump oil.
2. Description of the Prior Art
Apparatuses are known for heating the operator's cabin of a machine driven by an internal combustion engine and more particularly the operator's cabin of a vehicle using the heat content of oil from the engine sump. Such apparatus generally includes a hydraulic pump driven by the internal combustion engine and a load element, such as a throttle valve, that is connected at the pump discharge. Such apparatus also generally comprise a fluid to air heat exchanger in the operator's cabin and which is hydraulically connected between the load element and the oil sump. All this is described in pending U.S. application Ser. No. 123,169, filed Feb. 20, 1980 in the name of Moser, et al, assigned commonly with the present application, and claiming priority from West German Patent Application No. P. 29 32 448.9.
An apparatus useful for heating the operator's cabin of a vehicle having a heat exchanger and which utilizes the heat of the lubricating oil is well-known and described in U.S. Pat. No. 4,136,824, corresponding to West German Patent No. P 26 23 621. Such devices, however, have the drawback that calorific power is available only when the engine is at normal operating temperatures, and such temperatures are generally available only when the engine carries a load. The same problem is encountered whether the engine is air of water-cooled. The apparatus described in said application Ser. No. 123,169 improved this state of affairs by providing a hydraulic pump and a load element, more particularly a throttle valve, upstream of the heat exchanger. One disadvantage from such an arrangement, however, is that the amount of heat generated by the throttle valve often causes the temperature to rise, and initially, this rise in temperature produces only a small thermal gradient in the heat exchanger. Thus, the heat contribution is small and mainly the oil in the oil sump and the engine parts are heated. This applies to the warm-up period and to all operating conditions during which the temperature of the lubricating oil in the sump lies below the temperature of the oil returned from the heat exchanger, such as, for example, during long no-load periods and when the outside temperature is low. Such runs counter to the goal of accelerated heating of the operator's cabin and does not justify the large amount of energy expended in the hydraulic- pump drive.